Moving picture encoding apparatus and moving picture decoding apparatus in compliance with moving picture encoding methods described in Non-Patent Document 1 (ISO/IEC 14496-10:2004 Advanced Video Coding) and Non-Patent Document 2 (ISO/IEC 14496-10:2006/FPDAM3 Scalable Video Coding) have been known as background art realizing highly efficient coding and decoding utilizing spatial and temporal correlations of moving pictures.
Such methods of moving picture coding will be described in the following. First, the moving picture encoding method described in Non-Patent Document 1 (hereinafter referred to as Background Art 1) will be described. The moving picture encoding method of Background Art 1 is intra-prediction coding in which a predicted image of a block as an object of coding is generated through intra-prediction using locally decoded images of previously-encoded neighboring blocks, and coding is done using the predicted image. The method will be described more specifically in the following.
FIG. 6 is a block diagram of the moving picture encoding apparatus utilizing Background Art 1. Referring to FIG. 6, the moving picture encoding apparatus utilizing Background Art 1 includes an intra-prediction unit 1, an orthogonal transformation unit 2, a quantization unit 3, an inverse quantization unit 4, an inverse orthogonal transformation unit 5, a frame memory 6, and a variable length coding unit 9.
Intra-prediction unit 1 performs intra-prediction utilizing spatial correlation of images, and thereby generates a predicted image. Orthogonal transformation unit 2 orthogonally transforms input data. Quantization unit 3 quantizes input data. Inverse quantization unit 4 performs inverse quantization that is an operation reverse to that of quantization unit 3. Inverse orthogonal transformation unit 5 performs inverse orthogonal transformation that is an operation reverse to that of orthogonal transformation unit 2. Frame memory 6 temporarily stores images. Variable length coding unit 9 performs variable length coding on input data.
The moving picture encoding apparatus of Background Art 1 shown in FIG. 6 operates in the following manner.
<Step 501>
An image as an object of coding is divided to blocks of a prescribed size (blocks each of M×M pixels), and each block (hereinafter referred to as an object block of coding) is input to the moving picture encoding apparatus.
<Step 502>
Intra-prediction unit 1 generates a predicted image (a block of M×M pixels) corresponding to the input object block of coding.
The predicted image is generated by intra-prediction using locally decoded images of previously-encoded neighboring blocks stored in frame memory 6. The “previously-encoded neighboring blocks” refer to blocks of M×M pixels that have been already encoded at a stage preceding by one the present object block of coding (the block of M×M pixels), that is, four blocks of M×M pixels that have been locally decoded, at the left, above, upper left and upper right positions of the object block of coding.
<Step 503>
Prediction residue data (a block of M×M pixels) representing difference between the object block of coding and the predicted image of the block is input to orthogonal transformation unit 2 and quantization unit 3 in this order, and subjected to orthogonal transformation and quantization, respectively.
<Step 504>
Further, the quantized prediction residue data is locally decoded through processes at inverse quantization unit 4 and inverse orthogonal transformation unit 5, and then synthesized with the predicted image generated at step 502, whereby it is stored as the locally decoded image (a block of M×M pixels) of the object block of coding, in frame memory 6.
<Step 505>
The quantized prediction residue data is also input to variable length coding unit 9 and subjected to variable length coding, and then output as coded data.
<Step 506>
Steps 501 to 505 are repeated on all object blocks of coding forming the image as the object of coding.
The encoding process of Background Art 1 is realized through the process steps as described above, where intra-prediction by intra-prediction unit 1 and orthogonal transformation by orthogonal transformation unit 2 reduce spatial redundancy of the image as the object of coding, providing efficient coding.
The moving picture encoding method described in Non-Patent Document 2 (hereinafter referred to as Background Art 2) will be described. According to Background Art 2, coding is done utilizing so-called hierarchical encoding. Specifically, hierarchical encoding process is adopted, in which the block as the object of coding is subjected to inter-layer prediction predicting a layer as the object of coding utilizing inter-layer redundancy based on information of previously coded layers, and coding is done using the predicted image.
FIG. 7 shows a block diagram of the moving picture encoding apparatus utilizing Background Art 2. Referring to FIG. 7, the moving picture encoding apparatus utilizing Background Art 2 further includes a down-sampling unit 7, an up-sampling unit 8, change-over switches 10, a filtering unit 13, and a layer switching control unit 14.
Down-sampling unit 7 generates a reduced image by thinning-out pixels of an input image. Up-sampling unit 8 generates an enlarged image by interpolating pixels to the input image. Change-over switch 10b switches and outputs two types of input data in accordance with prescribed conditions. Filtering unit 13 performs low-pass filtering on the input image. Layer switching control unit 14 controls switching of layers as the object of coding.
Other components are the same as those of moving picture encoding apparatus shown in FIG. 6 and, therefore, description thereof will not be repeated. Since there are a plurality of change-over switches 10 in the figure, these will be identified by suffixes a and b. In the following, where there are a plurality of same elements, each will be identified in the similar manner.
The moving picture encoding apparatus in accordance with Background Art 2 shown in FIG. 7 operates in the following manner. In the following, only an example in which the object image of coding is encoded in a hierarchical manner in upper and lower two layers will be described. The upper layer of hierarchy is adopted to include high frequency and low frequency components, while the lower layer is adopted to include only the low frequency component. By way of example, when a VGA image (640×480 pixels) is to be hierarchically encoded in two layers, the VGA image is used as the upper layer and a QVGA image (320×240 pixels) that is generated by reducing the image of the upper layer is used as the lower layer.
<Step 601>
First, in order to encode the lower layer, layer switching control unit 14 controls change-over switches 10a and 10b. A reduced image output from down-sampling unit 7 is selected as the output of change-over switch 10a, and a predicted image output from intra-prediction unit 1 is selected as the output of change-over switch 10b. 
<Step 602>
The object image of coding is divided to blocks of a prescribed size (blocks each of N×N pixels), and each block (hereinafter referred to as object block of coding) is input to the moving picture encoding apparatus.
<Step 603>
The object block of coding is subjected to low-pass filtering at filtering unit 13, and then, a reduced image (a block of M×M pixels) corresponding to the object block of coding is generated at down-sampling unit 7. Here, the integers N and M representing the block size satisfy the relation of N=αM (α is an arbitrary integer).
<Step 604>
Intra-prediction unit 1 generates a predicted image (a block of M×M pixels) corresponding to the reduced image generated at step 603.
The predicted image is generated by performing intra-prediction similar to that of Background Art 1, on the locally decoded images (lower layer) of previously-encoded neighboring blocks stored in frame memory 6.
<Step 605>
Prediction residue data (a block of M×M pixels) representing difference between the reduced image generated at step 603 and the predicted image of the corresponding block is input to orthogonal transformation unit 2 and quantization unit 3 in this order, and orthogonal transformation and quantization are executed, respectively.
<Step 606>
Further, the quantized prediction residue data is locally decoded through processes at inverse quantization unit 4 and inverse orthogonal transformation unit 5, and then synthesized with the predicted image generated at step 604, whereby it is stored as a locally decoded image (a block of M×M pixels) of the object block of coding, in frame memory 6.
<Step 607>
Further, the quantized prediction residue data is also input to variable length coding unit 9 and subjected to variable length coding, and output as coded data.
<Step 608>
Steps 601 to 607 are repeated on all object blocks of coding forming the image as the object of coding.
<Step 609>
Next, for encoding the upper layer, layer switching control unit 14 controls change-over switches 10a and 10b. The object image of coding is selected as the output of change-over switch 10a and the enlarged image output from up-sampling unit 8 is selected as the output of change-over switch 10b, respectively.
<Step 610>
The object image of coding is divided to blocks of a prescribed size (blocks each of M×M pixels), and each block (hereinafter referred to as the object block of coding) is again input to the moving picture encoding apparatus.
<Step 611>
Up-sampling unit 8 generates, based on the locally decoded image of the lower layer corresponding to the object block of coding stored in frame memory 6, an enlarged image (a block of M×M pixels) corresponding to the block, by interpolation. The enlarged image is output as the predicted image of object block of coding.
<Step 612>
Prediction residue data (a block of M×M pixels) representing difference between the object block of coding and the predicted image obtained by the inter-layer prediction is input to orthogonal transformation unit 2 and quantization unit 3 in this order, and orthogonal transformation and quantization are executed, respectively.
<Step 613>
Further, the quantized prediction residue data is locally decoded through processes at inverse quantization unit 4 and inverse orthogonal transformation unit 5, and then synthesized with the predicted image generated at step 611, whereby it is stored as a locally decoded image (a block of M×M pixels) of the object block of coding, in frame memory 6.
<Step 614>
Further, the quantized prediction residue data is also input to variable length coding unit 9 and subjected to variable length coding, and output as coded data.
<Step 615>
Steps 609 to 614 are repeated on all object blocks of coding forming the image as the object of coding.
Encoding in accordance with Background Art 2 is realized by the processes described above. In the moving picture encoding apparatus in accordance with Background Art 2, the object image of coding PicA is reduced, and the reduced image Pica is encoded through process steps similar to those of Background Art 1. The reduced image is subjected to intra-prediction and orthogonal transformation, and therefore, it is possible to utilize spatial correlation of wider range of image than in Background Art 1.
For the encoding of upper layer, inter-layer prediction is performed in which an image PicB obtained by enlarging an image Picb resulting from coding/decoding of lower layer is used as the predicted image, so that prediction of higher accuracy than prediction of PicA in accordance with Background Art 1 becomes possible. Non-Patent Document 1: ISO/IEC 14496-10:2004 Advanced Video Coding Non-Patent Document 2: ISO/IEC 14496-10:2006/FPDAM3 Scalable Video Coding.